Yan Hui Wang

Synthesis and characterization of core-shell structural MWNT-zirconia nanocomposites.

Core-shell structural MWNT/ZrO2 nanocomposites were successfully prepared by one-step hydrolyzing of MWNT-dispersed ZrOCl2.8H2O aqueous solution. A highly conformal and uniform monoclinic zirconia coating was deposited on MWNTs by this new and simple method, and the thickness of the coating increased with the reaction time.

Microstructure and thermal characteristic of Si-coated multi-walled carbon nanotubes

The carbon nanotube (CNT) is a promising reinforcement material for manufacturing metal-or ceramic-based composites. However, CNTs are prone to interact with the matrix in a reactive atmosphere that often alters the structure and properties of CNTs and depresses their reinforcing effect. To overcome this problem, a protective silicon layer has been deposited on multi-walled carbon nanotubes (MWNTs) using cycled vacuum-feeding chemical vapour deposition by the in situ decomposition of gaseous SiH4. The silicon coating is well covered and continuous with a cubic-phase structure. It effectively improves the thermal stability of MWNTs by acting as a protective film, which inhibits and delays the onset of oxidation. Thermogravimetric analysis (TGA) reveals that the oxidation of Si-coated MWNTs occurs at a temperature of 676.3 °C, which is 105.1 °C higher than that of uncoated MWNTs, and the weight loss decreases with the increasing thickness of silicon coating.

Structure and Properties of Diamond Grits Coated with Corundum Micron Powders

Diamond is widely applied in cutting and grinding tools as the hardest and anti-wear material. Coating diamond surface with suitable materials is an effective method to improve the adhesion between diamond and matrix. Corundum-coated diamond, a new kind of diamond abrasive is developed for resin bond grinding applications. Diamond grits are coated with the corundum micron powders by the binding of a kind of vitreous material. The very rough and spiny morphology of the coated grit gives outstanding bond retention in resin matrix and avoids the premature loss of diamond from tools. The strength and oxidation resistance of diamond grits improve due to the coating protection effect. Industrial test results show that the grinding efficiency with an abrasive wheel made with corundum-coated diamond grits increases by more than 30% and the life of the wheel increases by 30~35%. Introduction Diamond grits give superior cutting performance for machining of rock and other nonferrous materials. The great attentions have been focused on the wear of diamond-segmented tools and the choice of bond type [1-4]. However, the waste of expensive grits associated with premature loss from tools is unexpected for toolmakers and users. One effective way to improve the adhesion between diamond and matrix is to coat diamond surface with suitable materials. Two types metals are usually selected as coating materials. One is carbide-forming metal as titanium, tungsten etc, which can form chemical bond between diamond and metal matrix [5-9]. Diamond grits coated with above materials have been developed for metal bond tools. The other is the metal such as nickel or copper. The thick coating layer of the metal assists the retention of diamond grits by keying into the bond. Cu, Ni-coated diamond grits are suitable for resin bond application. The metal coating, like Cu or Ni, can mechanically grip the friable grit to reduce its pullout and improve the adhesive strength between the grit and resin bond, thereby increasing the tool life greatly. However, designed for resin bond grinding wheels, the irregular friable grit is necessary for self-sharpening ability, which ensures the presence of new sharp cutting edges and keeps free cutting. The thick tough coating lowers the grit friability and cutting efficiency. The aim of this paper is to seek a suitable coating material that possesses the advantages of Cu or Ni coating and has no hurts to self-sharpening property. A new method has been developed to coat diamond with corundum micron powders, which are of low toughness and high strength. It is hoped that the new coating can meet all above-mentioned requirements. The coating process and the properties of corundum-coated diamond are introduced in this paper. Experimental Coating Process. Diamond grits were mixed with fine borosilicate glass powders; a thin layer of glass powders homogeneously bound on diamond surface, and then covered with corundum micro-powders. Various sizes of corundum micro-powders were selected to determine the effect of corundum particles on the coating properties. Table1 shows the range of glass compositions. The Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 250, pp 94-98 doi:10.4028/www.scientific.net/KEM.250.94

Study of the Properties and Application of Ti-Coated Diamond by Measuring Resistance

To improve the bond between diamond and metal matrix in cutting or grindi ng tools, one effective way is to coat diamond grits with carbide forming ele m nt, titanium. In this paper, a new assessing method for the properties of Ti-coated diamonds is establi shed by measuring the resistance. The relationships between the resistance and diamond grade, coating te mperature, oxidizing temperature are discussed respectively. The results show that the resistance of Ti-coated diamond grits is mainly determined by the coating thickness and crystal shape. The resistance reduces with the increasing of the coating thickness. The more irregular the cryst al, that is, the lower the grade, the smaller the resistance. For Ti-coated diamond in the order of SMD, BD and RVD, the corresponding resistance values are 21.2 Ω, 15.8 Ω, 12.3 Ω, respectively. The increasing of coating thickness with the rising of coating temperature results in the l ow resistance. The start oxidizing temperature can be indicated by the sudden change of the resistance of Ti-coated diamond g r ts. Introduction Diamond is widely applied in cutting and grinding tools as the hardest and anti-wear m at rials [1-8]. The diamond grits must be embedded into a bond when used in tools. Metal bond is a majority choice for most cases. The contact and adhesion of diamond with metal is an important factor o govern the performance and the life of tools. Due to the chemical inertness of diamond, it is very difficult to make diamond be strongly adhered with metal matrix. Diamond particle s easily pull out from metal matrix once subjecting to cutting forces. Coating diamond with the ca rbide forming metal such as Ti, Cr, Mo, and W etc is an effective way to improve the bond strength bet ween diamond and metal matrix [9-10]. The coating quality has great effects on the propert ies of coated diamond. Thus, the evaluation method for metal coating is necessary to control the coat ing process and properly use the coated grits. It is well known that pure diamond is a superior insulated material, but it turns to a conductor after being coated with a conductive coating. The conductibility is mainly det ermined by the coating properties. This paper introduced a method to measure the Ti-coated diam on resistance and discussed relationships between the resistance and diamond grade, coati ng temperature, oxidizing temperature. Experimental Experimental Principle. An instrument is designed for measuring resistance of the Ti-coat ed diamond grits. The schematic diagram of the instrument is shown in F ig.1. Place a coated diamond grit between two anvils on which silver electrodes are welded, apply load for close contact of the grit with electrode, and the resistance value of Ti-coated diamond is measured by an ohmmete r. Resistance value R of a conductor is calculated according to the following equation: S L R ρ = . (1) Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 250, pp 78-82 doi:10.4028/www.scientific.net/KEM.250.78

Relationship of Interface Microstructure and Adhesion Strength between Ti Coating and Diamond

Diamonds deposited with carbide forming element Ti were prepared by two methods of magnetron sputtering technique and vacuum slow vapor deposition. For the former , the interface reaction between Ti coating and diamond occurs during post-deposition anneali ng process whereas the same reaction occurs simultaneously within deposition process when using the latter method. The growth mechanism of TiC layer in the coating is investigated. The eff ct of the interface microstructure on the adhesion strength between Ti coating and diamond wa s etermined by the coating thickness and the morphology. Test results show that the interf ace reaction between Ti coating and diamond commences with TiC islets, which grow along the interfac e as reaction time increases. A continuous TiC film forms on diamond surface when diamond coated with Ti by magnetron sputtering technique is annealed at 800 for 1.5 h, and the maximum interface bond strength of 85 MPa is obtained. The vacuum slow vapor deposition method is developed based on the above results. XRD and AFM results confirm that a thin continuous TiC layer forms in a controlled manner during deposition process, the bond strength at the interface is higher than 140 M Pa. The metallurgical bond between diamond and the bond is realized at the aid of the metallic coating. Introduction Nearly all uses of diamond require fixing the crystals onto or int a medium. A classical method producing diamond tools used in grinding, sawing, drilling, cutting applications is to mount grits into metal matrix [1-7]. But the adhesion of binder metals and grits is poor because of no chemical interactions at the interface. The bonding strength of interface only depends on the mechanical support of metal matrix. The diamond grits will easily drop off fr om the matrix when subjected to high cutting force during operation process. In addition ferrous elements in low-melting binder will decrease the diamond strength due to graphitization. It is evident that strong bonding to diamond needs chemical, covalent inter action at the interface. Experiments have shown that if carbide-forming metals such as Ti, Zr, V, Cr, are deposited on diamond surfaces and heated to a sufficiently high temperature, carbide can b formed [8-11]. These elements are known to react easily with carbon and produce stable ca r ides, i.e. form the strong carbon-metal bonds for good adhesion. Sputtering deposition combining with anneali ng treatment is an effective way to realize the metallization of diamond. However, the mechanism of carbide growth on the interface is not completely clear. In this paper, the react ions at diamond/Ti interface and the growth of TiC during annealing process are investigated. The relati onship between bond strength and interface microstructure is discussed. Based on above results, the va cuum slow vapor deposition has been developed specially for coating diamond with carbide forming eleme nts such as Ti, Cr, W, Mo etc. and their alloys. Relationship of interface microstructure and adhesion strength between Ti coating and diamond is also investigated. Experiment Procedure Magnetron Sputtering Deposition. The surface of (111) of a large single crystal and 500 carats diamond abrasives of 50/60 US mesh were respectively deposited metal Ti using magnetic sputtering Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 250, pp 41-45 doi:10.4028/www.scientific.net/KEM.250.41

Ti Coating of Nanocrystalline Diamond by Atomic Layer Deposition

Nanocrystalline diamond compact possesses not only the advantageous performance of polycrystalline diamond but also the high strength and the high toughness of nano-ceramics. However, single-phase nanocrystalline diamond compact is very difficult to sinter because of a huge amount of oxygen-containing and nitrogen-containing functional groups absorbed on the surface of nanocrystalline diamond. In this paper, atomic layer deposition (ALD) method has been used to coat nanocrystalline diamond with titanium, which will promote the bonding of nanocrystalline diamond as the bond in polycrystalline diamond. In vacuum, the H2 and TiCl4 reactants were employed alternately in an ABAB… binary reaction sequence to achieve Ti layer, which reacted with diamond matrix and formed TiC in the coating, realizing strong chemical bonding between the coating and the diamond. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were utilized to study the structure and the morphology of the coating. The results confirmed the formation of titanium carbide at the depositing temperature 500°C. The darker spots and strips observed on nanocrystalline diamond particles by TEM were proved to be TiC and the nucleation and subsequent growth of TiC preferentially occurred in the defects as twin zones and dislocation areas on diamond surfaces.

Study of the Wettability between Diamond Abrasive and Vitrified Bond with Low Melting Point and High Strength

The adhesion between diamond grits and the bond strongly influence the properties of diamond tools. Since diamond is covalent crystal, the high interfacial energy leads to the poor interface bonding between diamond grits and the bond. Furthermore, the sintering temperature of traditional vitrified bond is also very high because of the high refractoriness of alkalis containing in the bond, resulting in serious thermal damage to diamond grits. In this paper, a low melting point and high strength vitrified bond has been prepared mainly from borate glass, clay and lead glass. The bond is completely glassy above 850°C and the bending strength of the bond sintered at 850°C for 7 minutes is 125.7MPa with a 6.5:3.5 corundum/bond ratio. Moreover, this bond possesses good wettability with diamond abrasive from 600°C to 850°C.

Effect of Si and Ti Coating on Interface Bonding between Diamond and Fe-Based Metal Bond

Fe-based metal bond has been widely used in fabricating diamond tools recently since the production cost could be greatly reduced for the low price of iron. However, graphitizing elements such as Fe, Co and Ni in the matrix catalyze the transformation of diamond to graphite during high temperature sintering process, which significantly decreases the tool’s efficiency and lifetime. In this paper, Si and Ti coating were coated on diamond grits by quasi atomic layer deposition (QALD) and vacuum slow vapor deposition (VSVD) separately not only to protect diamond from erosion but also to promote the adhesion between diamond grits and the bond. Three-point bending experiment was taken to measure the bending strength of Fe-Cu-Sn-Ni based metal bond diamond blade. In comparison with uncoated diamond blade, the bending strength of coated diamond blade improves dramatically. The theoretic calculation shows that the interface bonding strength between diamond and the metal bond increases by 181.68MPa owing to the Si coating. The effect of Si and Ti coating on interface bonding between diamond and the bond under different sintering temperatures was also illuminated.

Electroplating Nickel-Iron Alloy on the Diamond Surface

Ni-coated diamond grits are widely used in resin-bonding diamond tools for that nickel coating could not only increase the surface roughness, but also improve retention of the diamond in the bond. However coating nickel on diamond surface is too expensive for the high price of metal nickel. In order to obtain cost-effective coating, barrel-plating method was used to coat nickel-iron alloy on the diamond surface in this paper. Nickel-iron alloy coating with iron content of 13.62~17.25wt% has been obtained and the iron content in the alloy coating can be adjusted by the content of Fe2+ in the electrolyte. Compared with the uncoated-diamond, the compressive fracture strength (CFS) of coated diamond tested by single grit method has a distinct increase and it becomes higher as the iron content increases in the coating. The coating possesses ferromagnetism and the magnetic intensity of alloy coating with high iron content is larger than that with low iron content.

Silicon Atomic Layer Deposition on Nanocrystalline Diamond

Single-phase nanocrystalline diamond composite is very difficult to sinter because of a huge amount of oxygen-containing and nitrogen-containing functional groups adsorbed on the surface of nanocrystalline diamond going against the yielding of diamond-to-diamond bonding. In this paper, silicon film was deposited on nanocrystalline diamond by means of atomic layer deposition (ALD) using silane as precursor, which would promote the sintering of nanocrystalline diamond as the bond. The structure and the morphology of Si-deposited nanocrystalline diamond were thoroughly studied by X-ray diffraction (XRD), high-resolution electron microscopy (HREM) and Fourier transform infrared (FTIR) spectra. The results confirmed that silicon film grew uniformly on every primary particle and functional groups adsorbed on the surface of nanocrystalline diamond were removed by this method.